1. Field of the Invention
The present invention relates to viscous fluid heaters having rotors that shear viscous fluid to generate heat.
2. Description of the Related Art
Viscous fluid heaters, which are operated by the drive force of automobile engines, have become widely used as an auxiliary heat source. A typical viscous heater is provided with a housing that accommodates a drive shaft and a rotor. The drive shaft is rotated about its axis by the drive force transmitted from the engine. The rotor is operably connected to the drive shaft. The drive shaft and the rotor are located within a heating chamber, which is defined in the housing. In the heating chamber, a slight clearance is provided between the surfaces of a rotor and the opposing walls of the heating chamber.
A viscous fluid (silicone oil is generally used) fills the heating chamber including the clearance. When the rotor is rotated, the viscous fluid surrounding the rotor is moved together with the rotor. The viscous fluid residing in the vicinity of the walls of the heating chamber adheres to the walls. Accordingly, the rotation of the rotor shears the viscous fluid. The shearing action causes friction between the moving and stationary parts of the viscous fluid and generates heat.
In such viscous fluid heaters, it is preferably that the clearance between the rotor surface and the wall surface of the heating chamber be as small as possible to enhance the heating efficiency during shearing of the viscous fluid. However, if the clearance is too small, the rotor may contact and slide against the wall of the heating chamber when rotated. This may cause damage of the rotor and other parts.